The present invention pertains to internal mold release compositions, to polyol compositions containing same and processes for preparing polymeric products.
Polyether polyurethane moldings are being increasingly used in the manufacture of automobiles, furniture and in home construction. Molded polyether polyurethanes are especially important because they are lightweight and are resistant to moisture, weather, temperature extremes, and aging. As an illustration, molded polyether polyurethane elastomers have become of special interest in the manufacture of force-reducing impact media such as safety impact bumpers for automotive vehicles and impact resistant automotive fascia.
The high demand for molded polyether polyurethane articles requires that they be produced in the largest numbers in the shortest possible time. Polyurethane-forming mixtures are eminently suited for mass production because the reactants are liquid, that is they are pumpable, and are quick-reacting. The problem has existed, however, in providing adequate mold release in the shortest possible time to take fullest advantage of the unique capabilities of the polyurethane systems.
Heretofore, release of molded articles from molds in which they have been formed has been achieved by coating the surface of the mold cavity with an agent which facilitates release of the molded article from the walls of the mold cavity. Procedures such as this are described in U.S. Pat. Nos. 3,694,530: 3,640,769: 3,624,190: 3,607,397 and 3,413,390. This method has certain disadvantages. The agent, after molding, adheres to the surface of the molded article thereby removing such from the surface of the mold. As the mold release agent is removed from the mold surface, it must therefore be replaced so as to provide continued release of the molded articles from the mold. The necessity for repeated additions of mold release agent results in higher costs due to low productivity as a result of the additional time incurred in applying such additional quantities of mold release agents to the mold surfaces.
In addition, mold build-up may become a problem, since a fine film of urethane is left in spot areas of the mold surface. This build-up on the surface of the mold cavity walls eventually covers and obscures any detail on the mold cavity surface desired to be imparted to the molded article. Also, the presence of the release agent adhering to the surface of the molded article can impede subsequent operations on the article, such as painting or adhering operations.
Additionally, the need to reapply the release agent after each molding or a limited number of moldings interrupts the molding operation and slows down output.
The use of internal mold release agents for use in molding polyurethane articles has been disclosed by Boden et al. in U.S. Pat. No. 3,726,952, Godlewski in U.S. Pat. 4,024,088, Bonin et al. in U.S. Pat. No. 4,098,731, Sparrow et al. in U.S. Pat. No. 4,130,698, Godlewski in U.S. Pat. No. 4,111,861, Kleimann et al. in U.S. Pat. No. 4,201,847 and Godlewski in U.S. Pat. No. 4,220,727.
Some of these internal mold release agents bleed or creep to the surface of the molded article. Some of these articles cannot be painted even after appropriate preparation steps for painting has been done. Others are incompatible with polyether polyols. Most of them seriously reduce the activity of the catalyst. Almost all show degradation of physical properties such as reduced elongation.
The use of the "salts" described in U.S. Pat. No. 3,726,952 have not been effective release agents for reaction injection molding (RIM). While showing release characteristics per se their use has demonstrated in a screening program wherein hand mixed formulations are cast into an open mold other serious problems, namely: (1) degradation of the tin catalyst employed in the formulation, (2) excessively long gel and cure time, and (3) poor physical properties. These problems are believed to be caused by the presence of free carboxylic acid. It is released from the salt by the reaction of the amine with the isocyanate, and it is believed that the presence of these free carboxylic acids, or any acid, interferes with the cure rate of the hydroxyl-isocyanate reaction to form a urethane structure as disclosed in J. Polymer Science, Polymer Chemistry Edition, Vol. 19, 381-388 (1981) John Wiley & Son, Inc.
The reactivity or catalyst kill problem can be overcome to a certain degree by using tertiary amines in place of primary or secondary amines. Both U.S. Pat. Nos. 3,726,952 and 4,098,731 describe this technique. Since isocyanates cannot react with tertiary amines the salt cannot be split: it thus remains neutral (the carboxylic acid is not free), hence, catalyst kill does not seem evident. The use of tertiary amines, however, often shows bleed out or exudation problems which in turn result in poor paint adhesion. Further, retention of physical properties is seldom possible because of either excess reactivity when using very catalytically active amines, or because of plasticizer effects brought about by excessively long tertiary amine molecules.
The technology of U.S. Pat. No. 4,111,861 states that polar metal compounds can be employed to overcome catalyst kill problems brought on by the presence of fatty carboxylic acids. It states that metal ions must be present in an amount sufficient to neutralize the acid. Reference is made to the use of the Bi, Pb, Na, Li, and K ion, with sodium carbonate, sodium oleate, and potassium laurate being exemplified. They also show sodium oleate alone to be an effective release agent. When evaluated in RIM polyol systems as a single additive, it failed to show adequate release characteristics in a screening program wherein hand mixed formulations were cast into an open mold.
Zinc stearate has long been known to be an effective release agent for most thermoplastics. It is also used in polyester sheet molding compounds. When evaluated in RIM polyol systems containing only hydroxyl groups as the active hydrogen-containing source, zinc stearate as a single additive failed to show adequate release characteristics in a screening program wherein hand mixed formulations were cast into an open mold. Zinc stearate was observed to dissolve in a mixture of oleoyl sarcosine and excess polyoxypropylene diamine of 400 MW and the resultant mixture performed as an effective mold release agent.
The present invention provides for an improvement in one or more of the following: (1) increased multiple release, (2) increased ease of release, (3) effective and very stable catalyst reactivity, and (4) minimally altered physical properties in molded parts.